Detecting and evaluating the activity and the health state of the heart is a common and important task for physicians and healthcare professionals in general. This applies to both, the human heart and the animal heart. There are currently several options for heart activity detection and evaluation. The ECG measurement has a long history in personal healthcare as the standard tool to assess the performance of a patient's electrical heart muscle excitation. More recent products give a patient insight in his cardiac stress level by heart rate variability analysis in small handheld devices. Still lacking today is a simultaneous detection of the ECG (electrical activation) and its translation into mechanical action by the heart muscle, which would enable a wide range of applications in clinical as well as in Personal Healthcare (PHC) scenarios. Problems in the mechanical heart motion analyzed together with the ECG information are related to cardiac stress and even serious cardio-vascular conditions. The pre-ejection period—defined as time difference of the ECG's Q-wave and aortic valve opening—has been found to be an indicator for mental stress in psychology (see for example the article by H. Boudoulas, et al., “Effect of increased Adrenergetic Activity on the Relationship Between Electrical and Mechanical Systole, Circulation 64, No. 1, 198, the disclosure of which being incorporated herein in its entirety) and is of particular relevance for blood pressure measurements based on the pulse wave methodology. For measurements of internal mechanical organ movements, state-of-the-art technologies are ultrasound, impedance cardiography, phonocardiography, or computed tomography (CT) and magnetic resonance tomography (MRT) imaging modalities. Most of these technologies are only applicable in PHC applications in a very limited number of cases. Some, like MR and CT are not applicable at all in PHC applications. Ultrasound measurements typically require trained personnel to position the probe over one of the windows that allow ultrasound to penetrate the body. Impedance cardiography requires the placement of several electrodes on a patient thorax, which is difficult for laymen. Although there are new upcoming opportunities with intelligent textiles, the effort for a spot measurement is still quite substantial. Phonocardiography is a well-established technique in the medical community and provides information via heart sounds on valve openings and closures as well as murmurs linked to serious conditions. In practice, it turns out that the placement of the microphones is rather difficult. Radar techniques have been investigated extensively for remote monitoring of a subject's heart rate and respiration rate in military and rescue applications. Furthermore, electromagnetic (EM) waves allow the registration of internal organ movements via the detection of the reflections at conductive boundary layers in the body. We have already shown that heart rate, breathing, vessel dilatation—suitable for pulse transit time measurements—and more sophisticated heart motion phases can be detected (see for example an article published by the inventors: J. Muehlsteff, et al. “The use of a two channel Doppler Radar Sensor for the detection of heart motion phases”, 2006, IEEE EMBC 2006, conference proceedings). The present document concerns the use of a Doppler radar sensor, e.g. type KMY24, formerly available from Infineon, as described in the above mentioned article published by the inventors. The entirety of the article J. Muehlsteff, et al. “The use of a two channel Doppler Radar Sensor for the detection of heart motion phases”, 2006, IEEE EMBC 2006, conference proceedings is incorporated herein by reference.
One of the problems that occur when a Doppler radar sensor is used for heart measurements with different subjects is the difference in body dimensions and the thickness of the layer of fat tissue. Body tissue has a high absorption coefficient for electromagnetic waves. Therefore, especially for overweight and obese subjects, the received Doppler radar signal is heavily attenuated. An increase in transmission power would compensate for this attenuation and would be required in order to have reliable diagnosable signals. However, increasing the power too much will render the sensor too sensitive and cause artifacts from movements outside the field of interest. Furthermore, in battery-powered applications, unnecessarily high power consumption should be avoided.
This application describes two embodiments that can be used to obtain maximal signal quality at the lowest possible electromagnetic radiation level and transmission power. It increases transmission power until a heart signal is recognized or makes use of external known movements to adjust transmission power to the optimal value.